We mention in passing that, in the time-invariant case of
REF  with \(B(t) = \) , our estimates in Lemmas
REF  and
REF  reduce to those in
[1]} and
[1]}, respectively. Another
related but less precise estimate is given in
[3]}.
The mathematical tools we have used to treat the general
time-varying case are quite different from the ones used in
[1]}, [3]}.
